The present invention relates to flexible and configurable circuits and to electromechanical switching for microwave circuits constructed from polymers. In particular, the present invention relates to the provision of multiple radio frequency phase shifters and attenuators having a low insertion loss for use in connection with an array of radiator elements.
Antennas are used to radiate and receive radio frequency signals. The transmission and reception of radio frequency signals is useful in a broad range of activities. For instance, radio wave communication systems are desirable where communications are transmitted over large distances. In addition, the transmission and reception of radio wave signals is useful in connection with obtaining position information regarding distant objects.
Various parameters of a radio frequency signal may be controlled in connection with an antenna for the transmission and reception of such a signal. For example, the amplitude or phase of a radio frequency signal may be selectively controlled. In addition, an antenna may itself be controlled to selectively transmit and receive a desired frequency or band of frequencies, while rejecting other frequencies. In order to selectively control parameters of a radio frequency signal or to control the characteristics of an antenna, configurable circuitry may be used. One type of antenna for transmitting and receiving radio frequency signals that often features configurable circuitry is the phased array antenna.
A phased array antenna includes a number of radiating elements. In a typical phased array antenna system, the radio frequency signal provided to (or received from) each radiator element may be separately controlled. Among the parameters of a radio frequency signal that may be controlled with respect to an individual radiator element are the amplitude of the phase of the signal provided to each radiating element. Controlling the amplitude of the signal allows the signal strength to be tapered across the array""s elements to provide a desired gain pattern. Controlling the phase of a plurality of radiator elements in a coordinated fashion allows the antenna to be electronically pointed in space. Accordingly, a phased array antenna may be pointing of an antenna beam by controlling the phase of radio frequency signals provided to individual radiator elements allows the antenna to scan its beam.
In order to provide an antenna in which a characteristic of the signal, such as the phase of the signal, is controlled, selectively configurable antenna circuitry is required. For example, to control the phase of a signal, delay lines may be selectively switched into or out of the feed circuitry used to supply the radio frequency signal to a corresponding radiator element. However, delay lines are disadvantageous for use in connection with mobile or space-based antenna applications. In addition, the use of delay lines requires the inclusion of electrical or mechanical switches in the antenna circuitry. Such switches can result in insertion losses, and increase the cost of the antenna system by requiring the placement of individual switches. Switches having moving parts also generally require additional steps to seal those parts from contaminants, increasing the cost of systems utilizing such switches.
Another approach for controlling the phase of radio frequency signals involves the use of tuned reflection circuits, such as a 90xc2x0 hybrid. In general, a 90xc2x0 hybrid features open circuit stubs of equal length to force a reflected signal to sum in phase at the output port of the reflection circuit and subtract at the input port. The phase shift imported to a signal by the reflection circuit can be altered by altering the electrical length of the stubs. For example, a positive-intrinsic-negative (PIN) diode or discrete mechanical switch may be used to connect the stub to an additional length of conductive material. However, the use of PIN diodes can result in significant insertion losses. In addition, the use of conventional electronic or mechanical switches requires that individual switches be positioned with respect to the stubs of the reflector circuit, and be interconnected to the phase shifter circuit and to control electronics. As can be appreciated, the process of positioning and interconnecting individual mechanical switches or PIN diodes is a time consuming, laborious process.
Another approach has been proposed for providing a phase shifter circuit for use in connection with spatial signal combiners, such as coplanar wave guides or slot line antenna circuits. According to this approach, a polyimide, beam type switch is used to selectively vary the effective length of a slot line. The moveable beam of the switch is formed by two parallel slots in a polyimide layer. An electrode on the beam electrically connects adjacent sides of the slot. A DC bias voltage is selectively applied to the beam, and in particular to the electrode on the beam, to control the distance of the beam from a substrate. However, because the electrode on the moveable beam does not provide a signal path that is distinct from the electrode, the beam type switch is not readily adaptable to non-slot line circuits. In particular, such switches are not adaptable for use with transmission line circuits, such as microstrip or strip line type antenna circuits, without the additional complexity and signal amplitude losses caused by filters needed to separate the radio frequency signals from the DC bias voltages.
Therefore, there is a need for a method and an apparatus for providing a configurable circuit for use in connection with a transmission line radio frequency circuit, such as a microstrip or stripline antenna circuit. In particular, there is a need for a method and an apparatus for providing a configurable circuit for use in connection with radio frequency transmission lines that can be manufactured efficiently, without requiring the placement and interconnection of individual electronic or mechanical switches. Furthermore, there is a need for a configurable circuit for use in connection with radio frequency transmission lines that features low insertion loss. In addition, there is a need for such a configurable circuit that is capable of being produced economically in relatively large sheets, for use in connection with array antennas having a relatively large surface area. There is also a need for configurable circuits having moveable parts that can be produced without incurring additional time and expense to seal those moving parts from the environment.
In accordance with the present invention, a flexible, configurable circuit for use in providing switching or variable capacitance using capacitive or metal to metal coupling is disclosed. Also disclosed is a method for economically producing configurable circuits. In general, a configurable circuit in accordance with the present invention is formed from layers of material. Certain layers of the material have formed thereon at least one component of the configurable circuit. The completed configurable circuit is formed by registering the various layers such that the components of the configurable circuit are placed in a defined relationship with one another, and interconnecting the layers to form an operable configurable circuit. The configurable circuit of the present invention may be useful in connection with circuits that may benefit from or require a variable capacitance or mechanical switching, including metal contact switching, provided by the present invention.
According to an embodiment of the present invention, a configurable circuit is provided having at least a first component formed on a first planar substrate. At least a second component is formed on a flexible, second planar substrate. Also formed on the second planar substrate is at least a first moveable cantilever. The first and second planar substrates are spaced apart from one another, for example by a spacer layer that is relieved in the area of the at least a first moveable cantilever, to allow the at least a first moveable cantilever to move relative to the first substrate. By registering and interconnecting the first and second planar materials such that the at least a first component and the at least a second component are in a defined relationship to one another, a configurable circuit element is formed. A provided spacer layer may comprise an adhesive for interconnecting the first and second substrates.
According to another embodiment of the present invention, multiple at least first components are formed on a first substrate, multiple at least second components are formed on a flexible second substrate, and multiple moveable cantilevers are formed on the second substrate. The first and second substrates are registered such that the multiple at least first components are placed in a defined relationship with the multiple at least second components. The first and second substrates are separated from one another, for example by a spacer layer that has been relieved in the areas of the moveable cantilevers. By interconnecting the first and second layers, multiple configurable circuit elements are formed. Furthermore, the multiple circuit elements are formed substantially simultaneously, in that they are all formed during registration and interconnection of the first and second layers.
According to yet another embodiment of the present invention, a third planar substrate, having formed thereon at least a third component of a configurable circuit element is provided. The third planar substrate may then be interconnected to the second planar substrate, such that the moveable component or components of the second layer are sealed from the outside environment. The second and third substrates may be separated from one another to promote movement of the moveable cantilever or cantilevers, for example by a spacer layer that has been relieved in the area of the moveable cantilever or cantilevers.
According to still another embodiment of the present invention, a configurable circuit is provided in connection with a phased array antenna apparatus. The antenna may include a first planar material, having formed thereon at least first components of a plurality of configurable circuit elements. At least second components of the configurable circuit elements may be formed on a flexible second material, in which incisions have been made to form a plurality of moveable cantilevers. The antenna may also include a third planar material, having formed thereon a plurality of radiator elements. The first, second and third materials are registered, such that each of the plurality of radiator elements and each of the at least second components are placed in a defined relationship with a corresponding one of the at least first components. In particular, the materials are aligned to achieve the desired correspondence between components and to interconnect each of the at least first components to a corresponding one of the radiator elements.
According to the method of the present invention, the layers of the antenna having a plurality of radiator elements and a plurality of integrated configurable circuit elements are formed using conventional printed circuit board manufacturing techniques. For example, conductive traces on each of the layers may be formed using conventional chemical or mechanical etching or deposition techniques. Furthermore, the layer of material on which the moveable cantilevers are formed may utilize a flexible substrate, such as a polyimide. According to still another embodiment of the present invention, all of the layers of the antenna assembly utilize flexible substrates and/or flexible materials, to provide a flexible, configurable circuit that may conform to a surface that is not planar.
According to another embodiment of the present invention, the surface area of the flexible, configurable circuit is approximately equal to the surface area of the layer on which associated antenna radiator elements are formed. According to still another embodiment of the present invention, the flexible, configurable circuit is formed without requiring the placement and interconnection of individual switches. In accordance with yet another embodiment of the present invention, the at least first components of the flexible, configurable circuit are formed substantially simultaneously. In addition, the at least second components of the flexible, configurable circuit are formed substantially simultaneously. In accordance with a further embodiment of the present invention, all aspects of the flexible, configurable circuit are completed substantially simultaneously when the layer having the at least first components is registered with and interconnected to the layer having at least second components.
According to still a further embodiment of the present invention, an additional layer is provided. The additional layer may comprise a planar fourth material on which additional components of each of a plurality of circuit elements are formed. This further embodiment allows the configurable circuit to provide additional operating modes. The provision of such an additional layer, with or without additional components, also results in a configurable circuit in which all of the moving parts are sealed, without requiring any additional packaging.
According to one embodiment of the present invention, configurable circuit elements are provided in connection with each antenna radiator element. Accordingly, the characteristics of the circuit interconnected to each radiator element may be individually controlled.
Based on the foregoing summary, a number of salient features of the present invention are readily discerned. A flexible, configurable circuit can be provided. The configurable circuit may include a variable capacitor and/or switch. The configurable circuit may be used in connection with an antenna, such as an antenna having a plurality of radiator elements. The configurable circuit features low insertion losses, and the ability to control aspects of a signal in connection with a selected antenna element. In addition, the configurable circuit may be produced economically, using conventional printed circuit board techniques, and without requiring the placement of discrete components. The configurable circuit may also provide moving parts that are sealed by the component layers of the configurable circuit, without requiring additional packaging. The flexible, configurable circuit is well suited for use in connection with antenna arrays having a relatively large surface area and in connection with antenna arrays that must conform to surfaces that are not planar.
Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings.